Today's known procedures to obtain uniform and parallel samples of staple fiber materials in the textile industry favor the selection of long fibers. As a result, the prepared fiber samples generally contain an artificially enlarged proportion of long fibers compared to the original product, thereby rendering spurious the measurements and tests to be carried out on the fiber sample.
The equipment described in the Swiss patent document A 488,187 is representative of the present state of the art: the fiber material is removed by means of a rake from a perforated drum system. Because of higher likelihood of seizing long fibers, such sampling leads to enrichment in long fibers in the sampled batch, i.e., a fiber length distribution pattern which is weighted in favor of the long fibers is obtained.
Again, in the known method of the Swiss patent document A 637,468 wherein the measurement of the length distribution of textile fibers is carried out by dissociating a fiber web in an air current by fixing the individual fibers on a revolving sifting drum and then by optically determining the fiber lengths, the measurements are in part spurious because stretching the fibers results from their having been wound around the drum. Accordingly it is impossible to obtain a representative length distribution pattern. Moreover, aspiration by the drum further falsifies the test results because small fibers are sucked inside the sifting drum and are not available for the measurements.